President of Brazil's Chamber of Deputies Eduardo Cunha participates in a session of the chamber in Brasilia, Brazil, September 22, 2015. REUTERS/Ueslei Marcelino

The probe threatens the political career of Cunha, the sole member of Congress with authority to take up impeachment requests filed against President Dilma Rousseff.

Cunha has leveraged his power over potential impeachment proceedings to neutralize Rousseff’s Workers’ Party on the 21-member committee, whose investigation could drag on until April.

Congressman Fausto Pinato of the Evangelical Christian PRB party, who is in charge of the case, said there were grounds to investigate a breach of conduct by Cunha, including evidence provided by Switzerland of accounts held by the speaker and his wife at the Julius Baer bank.

Prosecutors accused Cunha of receiving a $5 million kickback in the graft scheme uncovered at state-run oil company Petroleo Brasileiro SA. But Cunha in March told a congressional commission looking into the scandal that he had no bank accounts abroad.

Cunha, who is third in the line of presidential succession, maintains he never lied, although he has not explained the existence of the accounts or lavish credit card expenditures detailed by Swiss authorities to their Brazilian counterparts. His lawyers said they would present his defense to the ethics committee on Tuesday.

The ouster of Cunha, who has obstructed Rousseff’s legislative agenda since corruption charges were leveled at him, could improve the president’s chances of survival. Her popularity has sunk to single digits due to a severe recession and the corruption scandal engulfing Petrobras.

As evidence mounted against him, Cunha has lost control of the house and sway over his centrist PMDB party, the largest in Rousseff’s coalition, which is expected to distance itself from her at a party Congress on Tuesday.

The main opposition PSDB party, which had avoided criticizing Cunha over the bank accounts in the hope that he would start the impeachment of Rousseff, last week announced it would seek his removal.

Workers’ Party congressmen were instructed by party chief and former president Luiz Inacio Lula da Silva to avoid antagonizing Cunha to save Rousseff from impeachment, according to the Brasilia-based political consultancy Arko Advice.

But when push comes to shove in a final vote on Cunha’s fate on the house floor, the Workers’ Party will vote en masse against the speaker, Arko Advice said in a note to clients.